Are there age related discounts on this route and if so how are they obtained?
For youth=<26:
BUY online via b-rail.be in 2 steps-you can stay on the very same train:
1.BRU-Roosendaal, as GOPass1, for about 7,50 (=6 eur fixed price+supplmt for the last portion).
Normal single Roosendaal-Amsterdam (or any other NS-station)
Same reverse for return.
2.For seniors=>65:
ditto, but buy Senior return BRU-Rsd, about 9 eur (as its return-but 1 day-you pay 2x the supplmt. for Essen-Rsdaal). No discount for 60+ on NS, Unless you have a yearly senior-discountpass.
3.for anyone in jan. only on sat+sun:
B-rail offers the shoppingreturn-a 1 day return for 9eur between any 2 DOMEstic stations=last one is Essen, thus buy 3 tickets:
this return, a normal single Essen-Roosendaal, then NS as above.
All above tickets can be had as homeprint.
Even in other cases always check both through fare and break in Roosendaal on b-rail, avoid NS-HIspeed, as b-rail accepts any credcd without fuss and NS does not-or if it allows, charges extra and may then tell you that its a real paperticket and has to be sent to a Dutch adress.
PS fastest-except Thalys is MEGAbus-a British concern (Stagecoach) which has 2 daily coaches (coming off Paris) BRU(beside Central station)-Amsterdam in less as 3 hrs, fare from 1 or 5 eur-but mostly 15. Stops in AMS at Camping Zeeburg-a 12 min ride on tram 26 from Centraal, but beside that rather (un)famous camping, which also has cheap chalets. If you are not only train-oriented, you may try this on 1 way to compare.